1. Field of the Invention
The present invention is related to the transmission and reception of control information in wireless communication systems.
2. Description of the Related Art
Wireless communication systems convey (i.e., transmit and/or receive) information over communication channels whose characteristics vary with time. When communication channels have relatively good characteristics more information can be conveyed over a defined time period. As the characteristics of the communication channels worsen, less information can be conveyed over a defined time period. The information conveyed over the communication channels are adversely affected by various types of noises such as amplitude fading, frequency translation, phase jitter and interference from nearby transmission of the same or other communication systems. Channel coding is often applied to the information prior to transmission so that the information is less vulnerable to noise. Channel coding essentially adds redundancy to the information so that if a portion of the information is adversely affected, another portion can still be decoded at the receiving end. Some well known examples of channel coding are convolutional coding and block coding.
Wireless communication systems that support relatively high speed information services are typically designed with control information that are transmitted over feedback or signaling channels. The feedback channels contain control information (also called control/feedback information) transmitted by the receiver describing the current state of the communication channel over which the received information propagated. It is desirable to transmit information during times when channel conditions are relatively good. The control/feedback information from the receiver informs the transmitter when such good channel conditions exist and provides other system related information, such as timing information about the transmitted information. It is desirable for the receiver to receive information about the timing of the transmitted information because the receiver typically uses such timing information to schedule the transmission and/or reception of corresponding information over a traffic channel; the traffic channel is the communication channel over which information from users of the communication system are conveyed. Fast and reliable control information gives knowledge of the fast changing wireless channel and allows relatively good channel conditions to be exploited. Further, fast acknowledgement by the receiver enables the transmitter to quickly retransmit the information or transmit new information. It is therefore desirable to receive control information that is reliable and robust to noise as such feedback information is transmitted over channels having the same or similar time varying conditions.
In order to make the control information robust to noise, it is typically transmitted as a relatively short burst at relatively high power. The relatively short burst carries much information and is typically subjected to extra channel coding which translates to a signal that uses a relatively large amount of bandwidth. The overhead in power and bandwidth is typically addressed with a design compromise in which a lower information rate is used thus introducing latency in the reception of the control information, i.e., the information is spread out in time. One approach to resolving the high power and relatively large bandwidth requirements of the control information is to design a receiver that can extract information before the block of received information is completely decoded; this is called early decoding and is achieved by utilizing the likelihood metric for the decoding trellis tree. The decoding trellis is a data structure where each element represents a distinct block of information. For each block in the trellis the likelihood (i.e., the probability) that the received block of information is that particular block is calculated and the block having the highest probability is selected as the block that was received. However this technique suffers from three main disadvantages: (1) it applies only to convolutional coded information (2) it is still has relatively low reliability and cannot be used for error detection and (3) it works well only when the receiver knows the timing of the received information, i.e., the beginning of transmission of the information and how long has the transmission occurred; in most cases transmitting such timing information explicitly in-band increases the demand on bandwidth. What is therefore needed is a technique for transmitting signaling information over a feedback channel where the signaling information is reliable regardless of the type of coding used and such signaling information contains data about the timing of transmitted information.